In 2003, Frank Rijsberman, then head of the International Water Management Institute, expressed his concern: “If present trends continue, the livelihoods of one third of the world's population will be affected by water scarcity by 2025. We could be facing annual losses equivalent to the entire grain crops of India and the US combined.”

The message is unusual. Normally, “water scarcity” is associated with tap water — Rijsberman talked about crops.

The dimension of the problem outlined is vast: combined grain production in the US and India accounts for approximately 30 per cent of global cereal consumption.

Since then, the relevant trends have indeed changed — but not for the better. New factors, in particular the craze for biofuels, have added pressure on water supplies. To illustrate the link between food and water: it takes approximately one litre of water to produce one calorie's-worth of food crops. Actual water requirements differ according to crop, climate and efficiency of irrigation methods. Another crucial variable is diet.

While high proportions of meat in European and American diets have been the case for many years, this trend is catching on in emerging markets that have seen a rise in incomes. Meat, on average, requires ten times the water required per calorie. As a result, the average daily diet in California requires 6,000 litres of water in farming, against 3,000 litres in countries such as Tunisia or Egypt.

We have to focus on water use in agriculture if we think water shortages might become more serious. There is reason for concern. Water use for farming is rising as world population grows and diets change in developing countries. People there are no longer satisfied with two bowls of rice a day.

Already, in the most fertile regions, overuse of water, mainly for agriculture, has led to sinking water tables. Groundwater is no longer withdrawn to provide a buffer over the year but in a structural way, mainly because water is seen as a free good.

As if this were not enough, politicians have added biofuels as another drain on scarce water. Estimates say it takes up to 9,100 litres of water to grow the soy for one litre of biodiesel. Measured in calories, the energy market is 20 times bigger than the food market. So replacing only 5 per cent of energy use with biofuel would double water use in agriculture. What is meant to ease a serious environmental problem, climate change, is aggravating a more serious problem: water shortage.

I am convinced that we will run out of water long before we run out of fuel. Recent price rises for basic foods are a first warning.

But there are solutions. Many of these must start with correcting mistakes, such as ending subsidies for biofuels. It is crucial to use water more efficiently in farming. There is enough land and water to meet the needs of changing diets.

The water used for farming is still less than the natural renewal rate. Open markets, without subsidies, would help efficient water use — if water had a price, for instance, through water rights traded between farmers.

It is imperative to try to arrest the trend towards structural overuse of fresh water and the right policies will ultimately determine whether a global crisis of water and food shortage can be avoided.

— Peter Brabeck-Letmathe is chairman of Nestlé. This is the first in a series of guest commentaries

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